Answer:
36
Step-by-step explanation:
You want to find 20% of 180.
You know that 10% is 1/10, which can be computed by moving the decimal point 1 place to the left:
10% of 180. = 18.0
20% is twice as many as 10%, so ...
20% of 180 = 2 × (10% of 180) = 2 × 18 = 36
36 students are in the environmental club.